docs.joinmastodon.org

ActivityPub is the open, standardized protocol Mastodon uses to implement federation, and the fediverse ("federated universe") is the name for all websites that can communicate with each other over ActivityPub and the World Wide Web. In practice, this means a Mastodon server can talk not only to other Mastodon servers but also to other software that implements ActivityPub, so your account is not confined to one platform or one provider.

How the pieces fit together

Mastodon is a microblogging service: you publish small updates to a stream on your profile, with optional media such as pictures, audio, video, or polls, and you can follow friends and discover new ones.

Federation is the mechanism that connects these services. Instead of one central service that everyone uses, there are multiple services that any number of people can use. The Mastodon documentation places these on a spectrum:

A Mastodon website can operate alone, like a traditional website where people sign up, post messages, upload pictures, and talk to each other. Unlike a traditional website, Mastodon websites can interoperate, letting their users communicate across sites. The documentation's own comparison is email: you can send a message from Gmail to someone on Outlook, Fastmail, Protonmail, or any other provider as long as you know their address. Likewise, you can mention or message anyone on any website using their address.

ActivityPub is what makes that possible. It is the standardized, open protocol Mastodon uses to implement federation, and any software that implements federation via ActivityPub can communicate with Mastodon seamlessly — just as Mastodon websites communicate with one another.

What counts as the fediverse

The fediverse includes all Mastodon servers, but also other implementations that speak ActivityPub. The documentation names several:

• Pleroma — a modular microblogging engine
• Pixelfed — a federated image sharing platform for sharing and consuming media posts
• Misskey — microblogging alongside a customizable dashboard
• PeerTube — upload videos to channels
• Plume — publish longer-form articles
• And many more, including individual and personal websites

Because the fediverse has no brand of its own, you will more often hear "follow me on Mastodon" than "follow me on the fediverse," though the documentation notes the latter is technically more correct.

What this changes for you

Two practical consequences follow from the documentation:

• Choice of service provider and policy. Because Mastodon is just software that can power any website, the site you sign up on is a choice, not a given. Different providers can set different policies.
• Reach beyond Mastodon. Your posts and follows are not limited to Mastodon software. If a service implements ActivityPub, it can interoperate with your Mastodon account.

If you want to understand Mastodon's design before choosing a server, the key takeaway is that federation via ActivityPub is what separates it from centralized networks: the network is the collection of interoperating sites, not a single company's platform.

Mastodon is not a single social network you join; it is software that powers many independent websites that can talk to each other. That is the core difference from a centralized platform like Twitter, where one company runs one service that everyone uses. On Mastodon, you pick a server, but you can still follow and message people on other servers, similar to how a Gmail user can email someone on Outlook.

Centralized vs. federated vs. distributed

The Mastodon documentation frames this as a spectrum of centralization:

Mastodon sits in the federated category. Each Mastodon website can operate alone, like a traditional website: people sign up, post messages, upload pictures, and talk to each other. Unlike a traditional website, Mastodon sites can interoperate, letting their users communicate across servers.

What this means in practice

• You are not locked into one provider. Because Mastodon is software that can power any website, the choice of service provider and its policies is a separate decision from using Mastodon itself.
• Cross-server communication works by address. Just as you can send email from Gmail to Outlook, Fastmail, or Protonmail as long as you know the address, you can mention or message anyone on any Mastodon website using their address.
• The network is bigger than Mastodon. Mastodon uses the open ActivityPub protocol to implement federation. Any software that also implements federation via ActivityPub can communicate with Mastodon seamlessly.

The fediverse, not just Mastodon

The fediverse ("federated universe") is the name for all websites that can communicate with each other over ActivityPub and the World Wide Web. That includes all Mastodon servers plus other implementations:

• Pleroma — a modular microblogging engine
• Pixelfed — federated image sharing, for media posts
• Misskey — microblogging alongside a customizable dashboard
• PeerTube — upload videos to channels
• Plume — publish longer-form articles
• And many more, including individual and personal websites

Because the fediverse has no single brand, you will more often hear "follow me on Mastodon" than "follow me on the fediverse," though the latter is technically more correct.

The takeaway

If you are used to Twitter, the mental shift is this: there is no single Mastodon company, app, or server that defines the network. There are many servers running the same software, and they interoperate through an open protocol. Your account lives on one server, but your reach is not limited to it.

Federation means no single company runs Mastodon. Instead, independent websites ("servers" or "instances") each operate on their own, but they can interoperate so users on different servers can follow, mention, and message each other. In practice, this gives you two things at once: you pick which server hosts your account, and you can still reach people on other servers using an address, much like email. The trade-off is that your server's operator and its policies affect your experience, so the choice of provider matters.

The core mechanism: many sites, one conversation

The Mastodon documentation describes federation as a form of decentralization. Rather than one central service everyone uses, there are multiple services that any number of people can use.

Mastodon sits in the federated row. A Mastodon website can operate alone, like a traditional website where people sign up, post, upload pictures, and talk to each other. Unlike a traditional website, it can also interoperate with other Mastodon sites, letting their users communicate across servers.

What this changes for you day to day

You interact across servers using an address

The documentation's own analogy is email: just as you can send mail from Gmail to someone on Outlook, Fastmail, or Protonmail as long as you know their address, you can mention or message anyone on any Mastodon website using their address. You do not need an account on their server to reach them.

Your server choice carries real consequences

Because Mastodon is software that can power any website, the operator of the server you join sets its own rules and policies. The documentation lists "Choice of service provider and policy" as a practical implication of federation. In concrete terms, that means questions like moderation rules, content policies, and who runs the server are decided per server, not globally.

Federation extends beyond Mastodon

Mastodon implements federation through ActivityPub, a standardized, open protocol. Any software that also implements federation via ActivityPub can communicate with Mastodon just as Mastodon servers communicate with each other. The documentation names several examples:

• Pleroma, a modular microblogging engine
• Pixelfed, a federated image-sharing platform
• Misskey, microblogging plus a customizable dashboard
• PeerTube, for uploading videos to channels
• Plume, for longer-form articles

Together with individual and personal websites, these make up the fediverse, the name for all sites that can communicate over ActivityPub and the web. The documentation notes the fediverse has no brand of its own, which is why people say "follow me on Mastodon" even when the more technically correct phrasing would be "follow me on the fediverse."

How to use this when deciding

If you are choosing where to start, the practical steps are:

1. Recognize that your account lives on one server, but you are not confined to it. You can follow and talk to people elsewhere.
2. Treat server selection as a policy decision, not just a technical one. Since each server sets its own rules, read what the server you are considering says about moderation and operation.
3. Expect cross-server interaction to work like email. To reach someone, you use their address rather than searching a single global directory.

The main thing to verify before committing is the specific server's policies, because federation guarantees reachability across servers but does not guarantee that any two servers will treat content the same way.

docs.joinmastodon.org is the official documentation site for the Mastodon software. It is a reference site, not a Mastodon server: you cannot sign up, post, or follow anyone there. Use it when you want to understand how Mastodon works, how federation and ActivityPub fit together, or how to run and use a Mastodon server.

What the site covers

The documentation is organized around explaining Mastodon as software rather than promoting a particular server. Its opening section, "What is Mastodon?", walks through the core concepts:

• Microblogging — publishing small updates to a stream on your profile, with optional media such as pictures, audio, video, or polls.
• Federation — a form of decentralization where many independent services interoperate instead of one central service serving everyone.
• ActivityPub — the standardized, open protocol Mastodon uses to implement federation.

The site places these in context with a comparison of network structures:

The email analogy is the one the documentation leans on: just as you can send mail from Gmail to Outlook, Fastmail, or Protonmail, a Mastodon user can mention or message anyone on any participating website using their address.

Why the ActivityPub explanation matters

Mastodon is not the only software speaking ActivityPub. The documentation names several other implementations that can communicate with Mastodon servers:

• Pleroma — a modular microblogging engine
• Pixelfed — federated image sharing
• Misskey — microblogging plus a customizable dashboard
• PeerTube — video uploads to channels
• Plume — longer-form articles

Together these form the fediverse, the set of websites that can communicate over ActivityPub and the web. The documentation notes that "follow me on Mastodon" is more common than "follow me on the fediverse," even though the latter is technically more accurate.

Practical implications it raises

Because Mastodon is software that can power any website, the documentation points out that service provider and policy choices matter — the server you join sets rules you are subject to. It also includes a "Choose your path" section, which separates readers who want to use Mastodon from those who want to run a server.

When to use this site

Reach for docs.joinmastodon.org when you need:

• A definition of federation, ActivityPub, or the fediverse
• Guidance on running or administering a Mastodon instance
• An explanation of how Mastodon differs from centralized platforms

Skip it if you are looking for a server to join or an account to create — that happens on an individual Mastodon website, not on the documentation site.

The Mastodon documentation at docs.joinmastodon.org is organized around what you want to do, not around a single linear manual. The site's "Choose your path" section is the entry point: pick the path that matches your goal — using Mastodon as a person, or running and moderating your own server — and the docs route you into the relevant guides from there. If you are unsure, start by reading "What is Mastodon?" and the pages on microblogging, federation, and ActivityPub, because those concepts shape which path actually applies to you.

What the documentation covers before you choose

The opening pages establish vocabulary the rest of the docs assume you already have:

• Microblogging — publishing small updates to a stream on your profile, optionally with media such as pictures, audio, video, or polls. Mastodon lets you follow friends and discover new ones.
• Federation — a form of decentralization. Instead of one central service everyone uses, there are multiple services any number of people can use. The docs place centralized services (Twitter, Facebook, Instagram) at one end, federated ones (email, XMPP, phone networks, physical mail) in the middle, and distributed ones (BitTorrent, IPFS, Scuttlebutt) at the other.
• ActivityPub — the standardized, open protocol Mastodon uses to implement federation. Software that implements federation via ActivityPub can communicate with Mastodon seamlessly.
• The fediverse — "federated universe," the name for all websites that can communicate over ActivityPub and the web. That includes Mastodon servers plus other implementations: Pleroma, Pixelfed, Misskey, PeerTube, Plume, and personal websites.

A Mastodon website can operate alone like a traditional site — people sign up, post, upload pictures, and talk to each other. Unlike a traditional site, Mastodon sites interoperate, so you can mention or message anyone on any site using their address, the same way you email someone from Gmail to Outlook.

The two main paths

The practical fork in the documentation follows from a simple fact: Mastodon is software that can power any website. That means your path depends on whether you are a user of someone else's server or the operator of your own.

The docs note one consequence of this split explicitly: because Mastodon is just software powering any website, choice of service provider and policy matters to potential users. Different servers set different rules, and the documentation treats that as a decision you make rather than a default you inherit.

How to decide which path is yours

Work through these questions in order:

1. Do you already have an account on a Mastodon server? If yes, you are on the user path. If no, you still need to choose a server before most user guides apply — the docs' federation explanation is what makes that choice meaningful.
2. Do you want to communicate with people on other servers? This is normal on Mastodon, not an exception. If cross-server interaction is your goal, the federation and ActivityPub pages are required reading before anything else, because they explain why your address, not a central username, is how people find you.
3. Do you want to control policy, moderation, or hosting? That is the server path. It is a different kind of commitment from signing up, and the docs separate it for that reason.
4. Are you looking for a specific non-Mastodon platform? If you are interested in Pixelfed, PeerTube, Misskey, Pleroma, or Plume, note that these are separate implementations in the same fediverse. The Mastodon docs describe how they interoperate, not how to run them.

Common sticking points

• "Follow me on Mastodon" vs. "follow me on the fediverse." The docs point out that the fediverse has no brand of its own, so the first phrasing is more common even though the second is technically more correct. Do not let the terminology make you think you are choosing between separate networks — you are not.
• Assuming one central sign-up. There is no single Mastodon site to join. The federation model is the reason the docs spend time on the centralized/federated/distributed comparison before sending you anywhere.
• Skipping the concepts. The "Choose your path" orientation sits after the explanatory pages, not before them. Reading the microblog, federation, and ActivityPub sections first will make the path you pick much easier to follow.

If you only remember one thing: the documentation is split by role, and the role you pick determines everything else. Read the four concept pages, decide whether you are a user or an operator, then follow the matching path.